Plasticized synthetic rubber composition



i 55 lyst. The tempera Patented June 6, 1 939 UNITED STAT ruis'rrorzunsim'rna'rrc RUBBER comrosrrrou Peter J1 Wiesevich, Eli

dicial change ofname to Standard Oil Devel poration of Delaware I NoDrawing.

1 Claim. I

her a small amount of a plasticizer or softener to increase thepliability, durability and tack of the rubber composition as well as tofacilitate the, compounding both by aiding the dispersion of solids andby lubricating the mix, whereby less power is consumed in the mixing.Many types of softeners have been used in the prior art such asvegetable, animal, and mineral oils, greases, asphaltic fluxes, fattyacids,'rosin cumar 1 resins, tars, pitchesand waxes. The presentinvention involves primarily the preparation of a new and improved typeof softener as will be described morefully'hereinaften- The syntheticrubber stock which may be plas- 20 ticized with this new softening agentmay comprise any of the rubber substitutes with or without subsequentcuring, such as polyethylene sulfide, polymerized vinyl chloride oracetate orsynthetic rubbers prepared by polymerization of 25 syntheticdiolefins such as butadiene, isoprene, or chloroprene, etc. Incommercial practice a certain amount of reclaim rubber is often mixedwith-the fresh crude rubber and other ingredients are frequently addedsuch as fillers, reinforcers, vulcanizing agents, accelerators, anti-'-oxidants, etc. in addition to the softeners as already mentioned.

According to the present invention a novel type of softener is preparedwhich preferably is 5 a more or less plastic and elastic aliphatichydrocarbon compound having a high molecular weight such as between theapproximate limits of 800 to 5,000 or 10,000. or even 15,000, 100,- 000,200,000 or more (as determined by-Stau- 40 dingers viscosity method),which is substantially greater than that of paraffin wax generallyconsidered to be between about 250 and 400. These compounds preferablyhave a linear chemical structure which may be represented 45 .by analmost completely saturated extremely.

long chain of carbon atoms with alkyl groups such as methyl, etc.attached as side chains onto either all of the carbon atoms in the chainor else just one or certain ones such as every sec- 50 0nd or thirdcarbon atom. Polymers'of this general structure may be advantageouslyprepared by polymerizing iso-oleflnes (isobutylene, isoamylene, etc.) atlow temperature in the presence of a volatilizable inorganic halide ascatature may be between the ap- Iabeth, N. 1., now by in- Peter J.Gaylor, assignor opment Company, a cor- Application December 18, 1936,Serial No. 116,485

proximate limits 0 even lower, depending f 5 C. and -10 or -20 C. or

upon the particular catalyst used. As catalyst, boron fluoride has beenfound particularly satisfactory. Also boron fluoride mixed with hydrogenfluoride may be 5 used as well as phosphorus trifluoride or.pentafluoride and even aluminum chloride, preferably statu nascendi asobtain acted on by hydrogen chloride.- In the case of aluminum chloride,3 to 5% ofethe catalyst may 10 be .used whereas in the case of thepreviously mentioned catalyst, 1% or so may be sufficient.

.Suitable volatile or non-volatile diluent such as pentane or acommercialnaphtha, or a light or heavy oil which may later serve asadditional softener when incorporated into the rubber may be used.Inasmuch as such polymerizations are usually exothermic, it is generallydesirable to provide some means of cooling the reaction "chamber eitherexternally or internally. The

molecular weight may be readily controlled by the temperature andduration of the polymerization.

As a particular example of a preferred method of preparing such apolymer. is'obutylene is polymerized at a temperature of about -10 C. bybubbling boron fluoride gas through a solution of isobutylene dissolvedin propane. A polymer of about 4,000 to 6,000 molecular weight may beprepared in this manner and the volatile solvent is removed bydistillation, after which any catalyst remaining dissolved or suspendedin the liquid is removed by blowing with steam or by washing andkneading with water or dilute caus- I tic soda, leaving the colorlessplastic polymer residue. Polymers of lower or higher molecular weightare prepared by varying the purity of the isobutylene and thetemperature of polymerization.

described method have: a high viscosity index, i. e. they show arelatively little change in viscosity with temperature. This property ishighly desirable when the softener is to be compounded in certain typesof rubber goods where it is desirable to have relatively constantproperties of pliability and elasticity over a fairly wide range .intemperature. Hydrogenated rubber may also be used as a softener,although it is not quite as satisfactory as polyisobutylene. It is ofcourse understood that mixtures of the above described novel softenersmay be used, or one or more of them may be used in coniunc-' tion withknown softeners such as those men tioned previously.

ed when aluminum is Plasticizers prepared according to the abovecorporated inthe synthetic rubber before it is The amount of this newpolymerized hydrocarbon softener to be used .in making compounded rubbercompositions may vary over a wide range such as from 0.1 to 50% or evencon-- siderably more in case it is desired more to use rubber as astabilizing or body-giving agent for the plastic hydrocarbon polymer.However, whenused simply as a softener or plasticizer in ordinary rubbercompounding, approximately 0.1% to 1% or or possibly based on thecontent of rubber plus plasticizer in the mix,

'is preferred.

In order to have all of the ingredients properly mixed ,or blendedtogether, several different methods may be used, first of which ismixingon the usual rubber mill or Banbury mixer which comprisesessentially a series of steel rolls set fairly close together so thatthey effect a combined grinding and kneading action on the plasticrubber mass being mixed. Another method of mixing is to dissolve boththesynthetic rubber and thepolymerized hydrocarbon softener separatelyin'a suitable volatile solvent such as naphtha and then to mix these twosolutions, continuing the agitation while evaporating off dippingsolutions, if desired, to effect curing. Fill-- corporated any timebefore vulcanization into. batches which are to be subjected to thattreatthe solvent. If the mixing is not continued a separation of thematerials into two layers may .occur. If this product is to be'cured theusual curing agents and accelerators as well as other materials such asfillers, anti-oxidants, etc. may be admixed with the rubber and softenerbefore evaporation of the solvent and then the curing eiiected after thesolvent has been removed.

In the manufacture of dipped goods, these plas ticizing polymers may beadded directly to the dipping solution, or they may be used as aseparate dip in solutions of Varsol, naphtha, carbon tetrachloride,benzol, or similar solvents. Alternate dips of this material andsynthetic rubber can be'made in this manner if so desired. Sulfurchloride may be added to one of the alternate ers, reinforcers, coloredpigments, anti-oxidants and other known addition agents may, of course,be added to the dipping solution'or may be indissolved in the solvent toprovide a cement. Finished goods dipped from these cements may be curedor vulcanizedby any of the common methods known to the art.

The plastic hydrocarbon polymer may be inpounds such as boron fluoride;fiuoboric acid,

chlorostannic acid, etc. The latter materials may ,be designated ashalo-formed rubber. Use of such plasticizing polymers mayals be =made inthe manufacture of synthetic rubber articles from a synthetic latex. Inthis case, a suspension or emulsion of the polymer, such as isobutylenepolymer, may be made and employed separately, or in conjunction with, oradmixed with the latex emulsion. In this case the resulting mixture maybe used with any of the common methods of synthetic rubber deposition,

such as electrolytic deposition, or the use of' chemical coagulating:agents for the production of finished goods.

In the preparation of rubberized fabrics, the synthetic rubberimpregnated cloth may be coated with a layer of these plasticiz'ingpolymers, and vice versa, 1. e. the fabric may be coated first withthese polymers, as by dipping the goods in a solution thereof, andfollowing by a dip with rubber. Another outside layer of plasticizingpolymer may also be added .on the synthetic rubber coating. Also, theseplasticizing polymers and/or synthetic rubber, or mixtures of thetwo,may be calenderedor frictioned on to textile fabrics with any of themethods well known to the art.

Plasticized synthetic rubber compositions prepared according to thepresent invention not only have the usual properties imparted to suchcompositions by ordinary softeners but .they have the additionaladvantages that owing to their particularly inert nature they also serveto a certain extent as anti-oxidants and help to prevent sun-cracking ofthe compounded goods, Such plasticized synthetic rubber compositions maybe used for a wide variety of purposes as is well known in the art, butare especially suitable for use in manufacturing soft mouldedmechanicals, dipped goods and coated fabrics.

Although not intending the invention to be limited thereby, thefollowing specific examples are given to illustrate'commercialapplications of the invention:

Example 1 50 parts of polyisobutylene-of about 128,000 *molecular weightare milled with 50 parts of polymerized chloroprene containingsufficient vulcanizing agent and then pressed into a sheet andvulcanized at 320 F. The product has a a higher chemical stability.E'rdmple 2 flow may be prepared-in this manner, serving as an excellentgasket material.

Example 3 75 parts of polyisobutylene of about 128,000

average molecular weight are 'milled with parts of polychloroprene'containing a vulcanizing agent, pressed into a sheet and vulcanized. Alight colored chemically resistant plastic is producedwhich is softerthan polychlorprene.

Example 4 60 parts of polyisobutylene of 8000 average molecular weightare .milled with 40 parts of poly- 'chloroprene, 10 parts of carbonblack and 2 parts of .stearic acid. A superior plastic is producedsuitable for coating fabrics. Other materials such as rubber,waxes,'resins, soaps, organic acids, oxidation inhibitors, pigments,vulcanizing agents, plasticizing agents, fillers, and the like may beadded to the compositions herein described.- h a This application is acontinuation-in-part of my earlier application Serial No. 717,575 filedon March 27, 1934.

much lighter color than polychlorprene and has It not intended that theinvention be limited by any of the specific examples given hereinabovenor by any theories ofthe operation of the .5 Iclaim:

invention but only by the appended claim in zeneous moldable compositioncomprising polywhich it is intended to claim all inherent noveltymerized chioroprene intimately mixed with polyin the invention asbroadly as the prior art. ,merized isobutylene having anaverasemolecular permits. weight of above 800 as determined by the vis- &cosity method. 5 An oxidation stable and acid resistant homo- PETER J.WIEZEVICH.

